The invention relates to aircraft bypass gas-turbine engines.
More specifically this invention relates to a turbojet engine having a fan driven into rotation by a speed-reducing gear unit whose input is driven by a turbine shaft. The speed-reducing gear unit includes a planet gear affixed to the turbine shaft, a ring gear affixed to the fan and a plurality of satellite gears in operative engagement with the planet and ring gears. The plurality of satellite gears are mounted on a satellite-gear support affixed to the engine casing.
In order to achieve ever higher pressures, turbojet engines are designed with large suction inlets. Accordingly, fan blade sizes increase while being constrained by the critical speed of the blade tips. This criterion is the product of the fan radius and its rotational speed, and if the radius is increased while maintaining a constant circumferential speed of the blade tips, then the speed of rotation of a fan must be reduced. For that reason, a speed-reducing gear unit is mounted between the turbine shaft and the fan shaft.
Aerodynamic loads generated by the slant of fan blades generate axial loads which are absorbed by engine bearings and the engine casing. As the fan diameter is increased, these loads substantially rise and become difficult to control. Accordingly, both the diameter and the weight of the bearings absorbing these loads are increased, resulting in problems in integrating these components into the engine.
The objective of the invention is to create a turbojet engine of the kind cited above wherein the axial loads absorbed by the fan bearings are decreased.
The objective of the invention is realized in that the satellite gears include helical teeth that mesh with helical teeth of the ring gear such that the speed-reducing gear unit generates axial loads on the ring gear which partly compensate for the axial loads generated by the fan.
The dimensions of the fan bearings are selected such that they absorb the differential of the axial loads generated by the fan and by the speed-reducing gear unit.
The generation of axial loads along the periphery of the speed-reducing gear unit results in a tipping torque near each satellite gear. In order to compensate for this torque, an opposing torque is generated by radial loads located near the contacts between the satellite gears and the ring and planet gears, by constraining an axial offset between the mean positions of the ring gear and the planet gears.
In a very advantageous manner, the helical satellite-gear teeth cooperate with the helical teeth of the planet gear and results in the speed-reducing gear unit applying axial loads on the planet gear which partly compensate for the axial loads produced by the turbine.
In this manner the absorbed loads by the turbine bearings are reduced.
Accordingly, the satellite gears apply first axial loads to the ring gear and second axial loadsxe2x80x94which are oppositely directed and substantially equal to the first onesxe2x80x94to the planet gear, the resultant of the first and second axial loads applied to the shafts of the satellite gears, being substantially zero.
Other advantages and features of the invention are elucidated in the following illustrative description and in relation to the attached drawings.